<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div id="box">hello box
        <p>
            this is <b id="btag">tag</b>
        </p>
    </div>
    <script>
        console.log(document.body.children[0]);
        console.log(document.getElementById('box'));
        console.log(document.body.children[0].children[0].children[0]);
        console.log(document.getElementById('btag'));


    </script>
</body>

</html>